depletion rate　

depletion rate　折耗率　

rate of depletion；an accrual accounting method that companies use to allocate the cost of extracting natural resources such as timber，minerals and oil from the earth.Depletion is calculated for tax-deduction and bookkeeping purposes.Unlike depreciation and amortization，which mainly describe the deduction of expenses due to the aging of equipment and property，depletion is the actual physical depletion of natural resources by companies.